Consecutive "wait-serial" commands sometimes fail matching

[urish]

For example, in this scenario taken from platform-io-esp32-http-client:

name: HTTP Client Test
version: 1
author: Uri Shaked

steps:
  - wait-serial: 'Connecting to WiFi'
  - wait-serial: 'Fetching http://example.org... HTTP 200'
  - wait-serial: '<title>Example Domain</title>'

The matching fails in cases when two expected lines are returned in a single buffer (e.g. both Fetching http://example.org... HTTP 200 and <title>Example Domain</title> are returned in one buffer).